In new x-ray devices with C-arms adjustable in three dimensions for supporting x-ray imaging systems, as well as the pure x-ray imaging, positioning devices for positioning tools such as puncturing needles by means of laser fan beams generated by lasers are also used. As a result of their construction C-arms twist depending on the angulation selected. These torsions lead to unknown projection geometry and location of the laser positioning device. These devices are needed however in order to determine the location of the tools relative to the images acquired by the x-ray imaging system (2D or 3D) and to use them for positioning. Also, after the x-ray device has been in operation for a long period, the laser fan beams that were originally adjusted when the x-ray device was installed get out of adjustment. In particular vibrations caused by C-arm movements can lead to adjustment problems after long periods of operation.
To determine the x-ray geometry of the x-ray imaging system at the C-arm there are numerous systems known which calculate the projection geometry for a given object, especially a calibration phantom. This calculation is performed in a calibration sequence during the installation of the system in order to use the resulting parameters during operation with patients for 3D reconstruction and 2D/3D fusion. One such method is known for example from the article “Improving 3-D Image Quality of X-ray C-Arm Imaging Systems by Using Properly Designed Pose Determination Systems for Calibrating the Projection Geometry” by N. Strobel, B. Heigl, T. Brunner, O. Schütz, M. Mitschke, K. Wiesent and T. Mertelmeier, Medical Imaging 2003, Physics of Medical Imaging, Proceedings of the SPIE, Volume 5030, Pages 943 ff., 2003. Such a method however does not allow the location of the laser or of the laser fan beam relative to the x-ray geometry to be determined, since the location of a laser fan beam cannot be recorded in the x-ray image.